The present invention relates generally to communications, and more specifically to improvements in Integrated Circuits for use in Radio Frequency applications.
Many communication systems modulate electromagnetic signals from baseband to higher frequencies for transmission, and subsequently demodulate those high frequencies back to their original frequency band when they reach the receiver. The original (or baseband) signal, may be, for example, data, voice or video. These baseband signals may be produced by transducers such as microphones or video cameras, be computer generated, or transferred from an electronic storage device. In general, the high frequencies provide longer range and higher capacity channels than baseband signals, and because high frequency (HF) radio frequency (RF) signals can effectively propagate through the air, they can be used for wireless transmissions as well as hard wired or fibre channels.
All of these signals are generally referred to as RF signals, which are electromagnetic signals; that is, waveforms with electrical and magnetic properties within the electromagnetic spectrum normally associated with radio wave propagation.
Wired communication systems which employ such modulation and demodulation techniques include computer communication systems such as local area networks (LANs), point-to-point communications, and wide area networks (WANs) such as the Internet. These networks generally communicate data signals over electrically conductive or optical fibre channels. Wireless communication systems which may employ modulation and demodulation include those for public broadcasting such as AM and FM radio, and UHF and VHF television. Private communication systems may include cellular telephone networks, personal paging devices, HF radio systems used by taxi services, microwave backbone networks, interconnected appliances under the Bluetooth standard, and satellite communications. Other wired and wireless systems which use RF modulation and demodulation would be known to those skilled in the art.
One of the current problems in the art is to develop effective mixers that can adapt to the varying requirements caused either by changing reception conditions, or even changing standards during the use of the device.
For cellular telephones, and similar consumer items, it is desirable to have transmitters and receivers (which may be referred to in combination as a transceiver) that can be fully integrated onto inexpensive, low power, integrated circuits (ICs).
This continuing desire to implement low-cost, power efficient receivers and transmitters has led to intensive research into the use of highly integrated designs, an increasingly important aspect for portable systems, including cellular telephone handsets. This has proven especially challenging as the frequencies of interest in the wireless telecommunications industry (especially low-power cellular/micro-cellular voice/data personal communications systems) have risen above those used previously (approximately 900 MHz) into the spectrum above 1 GHz.
Attempts to provide flexible designs in Radio Frequency Integrated Circuits (RFIC)xe2x80x94also known as monolithic microwave integrated circuits (MMIC)xe2x80x94allowing for multiple standards and varying conditions of reception have met with limited success. These designs usually provide duplication of the functions affected by these considerations. One example of prior art, U.S. Pat. No. 6,185,418 xe2x80x9cAdaptive digital radio communication systemxe2x80x9d, involves reconfiguring the system by reprogramming at least one programmable device such as a Programmable Logic Device (PLD) to perform the digital communications processing functions of the transmitter or the receiver of a radio communications system. Other implementations are related to the ability to distinguish between and cope with very different modulation schemes. One such example is given in U.S. Pat. No. 5,649,288 xe2x80x9cDual-function double balanced mixer circuitxe2x80x9d.
It is known and understood in the art that the ability to deal with multiple transmission standards within a single IC design presents some difficulties in high density radio frequency integrated circuit (RF IC) technologies. These difficulties have lead circuit designers to provide separate circuit subsystems for those elements to ensure sufficiently high performance, thereby effectively introducing a degree of duplication of function. This duplication is not conducive to lower costs and reduced power consumption, important considerations in the domain of interest. The invention is especially important in the personal communications industry (low-powerxe2x80x94cellular/micro-cellular voice/data) as the number of standards in common use has increased, and the demand for improved performance at a lower price has been met. The present invention mitigates the disadvantages of previous designs and provides other benefits, as will be apparent from the following figures and description.
The present invention provides a balanced active demodulator that simplifies the configuration and set-up of a balanced demodulator section and that reduces the labour or man-hours, and the time required during manufacture for adjusting the demodulation characteristics for optimum performance.
The present invention also provides a balanced demodulator that both decreases the number of components or parts required and lowers the fabrication cost. The invention provides a means to select various critical performance and standards parameters within a single receiver/transmitter design. It is therefore suitable for use in products in which cost-effectiveness is a critical factor such as those used in personal communications.
The circuit structure of the invention uses a single integrated circuit subsystem to replace a number of similar subsystems, each specifically designed for one standard, or designed to deal with a limited range of reception conditions. The result is that a cost-effective single design of receiver may be used in the wireless personal communication field or any other field where there are differing standards and reception requirements for a particular device or class of devices.
The invention introduces circuitry to allow various combinations of components to be selected either during use, or during configuration and set-up, or during both phases. Further, the invention comprises a number of selectable RF input stages, and a number of selectable current sources to provide bias to the selected RF input stage.
As a demonstration of the technology, the invention has been implemented as a multi-standard mixer that has been realized with a Radio Frequency Integrated Circuit (RFIC) process.